The refractive index of light with respect to the material composing a lens differs depending on the wavelength. Therefore, when various wavelengths of light enter the optical system of an imaging apparatus, axial chromatic aberration occurs, so that images of varying sharpnesses (i.e., how sharp the images are) may be obtained depending on the color. When a color of low sharpness is contained in the image, that color becomes a cause for image quality deterioration.
In an imaging apparatus such as a camera, if the position of a subject is contained within the depth of field, focusing is attained, whereby a clear image can be imaged. In order to enable imaging of subjects located at various positions, the imaging apparatus needs to separately have a means for detecting a focusing state and a means for making a focus adjustment.
In order to solve the aforementioned problems, a technique has been proposed which, by utilizing an axial chromatic aberration of the optical system, allows the sharpness of a first color component to be reflected on a second color component which is different from the first color component, thus achieving expansion of the depth of field and correction of the axial chromatic aberration (Patent Document 1). According to the method of Patent Document 1, by allowing the sharpness of the first color component to be reflected on the second color component, the sharpness of the second color component can be enhanced. As a result, the depth of field can be increased, whereby subjects at a greater variety of distances can be relatively clearly imaged, without making focus adjustments.